Surprise perfect matching of my 40m loop antenna with ladder line for 10m!

I had homebrewed a ladder line along with a full wave loop antenna for 40m using 60m long 2.5 sq mm insulated copper wire. ‘Steps’ of the ladder line were made using 2 inch long 6mm diameter black drip irrigation pipes which are UV protected. Black nylon ties which are again UV protected, were used to keep the ‘steps’ in position on the ladder line, at intervals of about 22 cm. Initially I had 10m long ladder line. As it was difficult to match for 40m, yesterday I removed 3 ‘steps’ which would reduce the length of ladder line by 66 cm. There was improved performance on 40m.

Today I removed another set of three ‘steps’ so that now the ladder line will be shorter by 132 cm and the loop antenna would have lengthened by a total of 264 cm. I am using a homebrew 4:1 balun at the junction between the ladder line and a 183 cm piece of HLF 200 cable to the shack. A homebrew common mode choke has been placed at its termination inside the shack.

Tuning is done first using my ATU-100 automatic external antenna tuner. When needed, for ‘touching up’ any residual SWR, I use the internal antenna tuner in my FT-710 radio. While doing so, the ‘AUTO’ mode in ATU-100 can be disabled.

After today’s revision in the ladder line, I was pleasantly surprised to see that the antenna system is perfectly matched for 10m without tuner! It was just 1.02 SWR on 28.010 MHz.

Checked on 28.200 MHz and found SWR to be 1.01, again, without tuner.

On 28.500 MHz, SWR was seen as 1.29 in ATU-100, while it appeared to be slightly above 1 in FT-710 radio.

SWR at 28.800 MHz was seen as 1.70 in ATU-100, and about 1.1 in the radio. So the low SWR bandwidth of the ladder line – loop antenna combination for 10m band with reasonable SWR is quite wide. I have never had it so in any of my previous antenna experiments. I do not have any specific explanation for this wonderful performance of my ladder line – loop antenna combination on 10m for the ‘bench test’. If it works out equally well in the ‘on-air’ performance, I can enjoy the coming 10m season due to winter anomaly expected to last a few months.

Tried a few CQ calls in CW to the check the pick up of my signals on the Reverse Beacon Network. I was happy to see pick up at VK6ANC in Australia, at 3985 miles at about 10.40 am, with a signal to noise ratio of 6 dB. Interestingly, pick up at VU2TUM and VR2FUN-77 were also at the same SNR.

Checked propagation from my setup on 10m using Reverse Beacon Network with CQ calls in CW again at about 12 noon. The longest distance had improved to 4129 miles, at IK7YTT. Interestingly, as day has progressed, direction of predominant propagation has changed towards Europe. This is exactly what VU2DSI had told me yesterday in detail during our QSO on 20m. He had mentioned that if you check in the morning, you will get stations towards the East like Australia, while you get stations from Europe in the afternoon. VU2DSI has a great deal of data on 10m propagation spanning over quarter century or more. He is analyzing that data in detail and hope to come out with a paper soon. That will be a great tool for radio amateurs to assess 10m propagation over decades.

Here you can see the display on ATU-100 when the CQ call is going on. Power is seen as 77W and SWR 1.05. Power at the antenna is shown as 77W with 99% antenna efficiency. That is very heartening see after putting in a lot of work into making the ladder line and loop antenna. Of course, this is an estimate by the firmware within the tuner and may not mean actual on air performance.

Checked propagation again at 4 pm IST and got results like that at 12 noon. I hope to have nice QSOs on 10m band during the peak activity in the coming winter. Shall be on the lookout for stations from Europe and Oceania in the coming weeks. I am aware that pick up on RBN need not always get converted to on air QSOs. But let us try!